A self-addressed envelope already has your own address written on it as the place to send it. You post it to someone — a company, an office, a person — they put a reply inside, and they can send it straight back to you without looking up where you live.

A self-addressed envelope already has your own address written on itself-addressed信封上已經寫好了你自己的地址 as the place to send it當作寄回去的地方 You post it to someone你把它寄給某個人 — a company, an office, a person ———公司、辦公室、或某個人—— they put a reply inside他們把回覆放進去 and they can send it straight back to you without looking up where you live就能直接寄回給你，不用去查你住哪裡

In older paper-form days this was very common; people often also stuck a stamp on it, and then it was a self-addressed stamped envelope, or SASE.

In older paper-form days this was very common在早期用紙本表格的年代這很常見 people often also stuck a stamp on it人們常常還會貼上郵票 and then it was a self-addressed stamped envelope, or SASE這樣就變成self-addressed stamped envelope，簡稱SASE

The 'self' is you, the person who wants the reply. Though actually, it is easy to picture the envelope addressing itself — it doesn't; you wrote the address.

The 'self' is you「self」指的就是你 the person who wants the reply也就是想收到回覆的那個人 Though actually不過其實 it is easy to picture the envelope addressing itself很容易讓人誤會成信封自己寫地址 — it doesn't——它並不會 you wrote the address是你自己寫上去的

The word is a bit formal and office-like, and less needed now that so many replies come by email.

The word is a bit formal and office-like這個字有點正式、有點公事公辦的感覺 and less needed now that so many replies come by email現在很多回覆都用email，也就比較不需要它了